PROJECT SUMMARY/ ABSTRACT It is becoming increasingly evident that the majority of the mammalian genome has the potential to express non-coding RNAs (ncRNAs). However, the functionality and mechanism(s) of regulation of these ncRNAs are just beginning to be explored. One challenge that biologists encounter is the detection of these ncRNAs, which often tend to be transcriptionally tightly controlled and rapidly degraded. We have recently identified a long noncoding (lnc) RNA expressing locus, known as lncRNA-CSR, that regulates DNA rearrangments in the Immunoglobulin heavy chain (IgH) locus of B cells. Using mouse model systems that lack lncRNA processing/degradation activity along with a combination with high throughput genomics, bioinformatics, and various ChIP-seq based experiments, we are able to predict long-range transcription enhancer function of the lncRNA-CSR locus. In this application, we continue to focus our investigation on the functionality of lncRNA-CSR and three other novel lncRNA expressing loci, that we propose to have a role in orchestrating DNA rearrangment events in germinal center resident B cells. B lymphocytes have the unique ability to undergo programmed somatic mutagenesis of their genomes (at immunoglobulin gene loci) to generate the diversity of antibodies required by our immune system to combat the plethora of antigens we might encounter, a process known as antibody diversification. However, as collateral damage emerging from this very unusual and useful ability to undertake beneficial somatic mutagenesis events is the ability of B cells accidently to mutate their genome at a very low frequency at various inappropriate locations. These accidental mutations are the cause of various B cell malignancies, particularly those that evolve from germinal center derived B cells. Interestingly, cancer-causing translocations in B cells occur at regions of divergent transcription?that is, promoters and enhancers?which exist inside topological domains of superenhancer clusters. We postulate that lncRNA-CSR is responsible for tethering long distant regulatory elements (i.e, promoters and enhancers) in the IgH locus superenhancer cluster to facilitate genome organization, transcription control of regulated genes, and, ultimately, to promote antibody diversification mechanisms without inducing cancer causing DNA alterations.